If you're not familiar with the retweet, it's basically a Twitter convention with which users pass on tweets that they like from other users. I say, "I've learned more from Lifehacker than from any of my college professors," and you say "RT @adampash I've learned more from Lifehacker than from any of my college professors." It's great for passing on a tweet you like, but retweets are pretty useless in search results.

Luckily Twitter search supports the common hyphen (-) operator, meaning NOT, for search terms. So to get a fresher batch of search results from Twitter minus the retweets, just add -RT to your query. As steven_noble points out, it's a great way, for example, to get more focused results on tweets regarding the Iran election minus the retweeting noise.